[2] In 1930 D. Napier & Son identified a market for light aircraft engines, noting that light aircraft cost much the same as their car and were being bought by much the same class of person.

Following a change of personnel, the engine was given the go-ahead in 1932, with aircraft manufacturer de Havilland identified as a likely customer.

[3] Unlike the later de Havilland Gipsy Six the poppet valves were operated by a single gear driven overhead camshaft.

[3] Development continued but only a few were sold for experimental and prototype aircraft.

By 1935 Napier needed to refocus their efforts and, with Halford's broadly similar but more powerful de Havilland Gipsy Six now on the market, the Javelin was withdrawn.